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The properties of symmetric nuclear matter are investigated in the nonlinear relativistic mean field theory of nuclear matter. We consider the constraints imposed by four nuclear ground state properties on the coupling constants and on the equation of state at zero and at finite temperature. We find that the compression constant K(ρ0) as well as the temperature is irrelevant for the stiffness of the equation of state for m*(ρ0)≤0.7. The main point is that the relativistic mean field theory exhibits acausal and unphysical behavior for compressibilities below K(ρ0)=200 MeV. Every set of coupling constants with a negative quartic coupling constant c is unstable against small quantum fluctuations.
We analyze the phase structure of the nonlinear mean-field meson theory of baryonic matter (nucleons plus delta resonances). Depending on the choice of the coupling constants, we find three physically distinct phase transitions in this theory: a nucleonic liquid-gas transition in the low temperature, Tc<20 MeV, low density, ρ≃0.5ρ0, regime, a high-temperature (T≃150 MeV) finite density transition from a gas of massive hadrons to a nearly massless baryon, antibaryon plasma, and, third, a strong phase transition from the nucleonic fluid to a resonance-dominated ‘‘delta-matter’’ isomer at ρ>2ρ0 and Tc<50 MeV. All three phase transitions are of first order. It is shown that the occurrence of these different phase transitions depends critically on the coupling constants. Since the production of pions also depends strongly on the coupling constants, it is seen that the equation of state cannot be derived unambiguously from pion data.
Die vorliegende Arbeit präsentiert Forschungsarbeiten basierend auf nanoskopischen Oberflächenmessungen an plasmonischen Metaoberflächen und zweidimensionalen Materialien, insbesondere dem halbleitenden Übergangsmetal-Dichalcogenid (TMDC) WS_2. Die Thesis ist in sieben Kapitel untergegliedert. Die Einleitung vermittelt einen Überblick über die treibenden Kräfte hinter der Forschung im Bereich der Nanophotonik an zweidimensionalen Materialsystemen. Die Untersuchung der Licht-Materie-Wechselwirkung an dünnen Materialgrenzflächen zieht sich als roter Faden durch die gesamte Arbeit.
Das zweite Kapitel beschreibt den experimentellen Aufbau, der für die Durchführung der nanoskopischen Messungen in dieser Arbeit implementiert wurde. Es werden theoretische Grundlagen, das Messprinzip und die Implementierung des optischen Rasternahfeldmikroskops (s-SNOM) skizziert. Außerdem wird ein Strom-Spannungs-Rasterkraftmikroskop (c-AFM) im Kontaktmodus genutzt, um elektrische Ströme auf mikroskopischen zweidimensionalen TMDC-Terrassen zu messen. In den darauffolgenden vier Kapiteln werden die Beiträge dieser Arbeit zur Untersuchung der Licht-Materie-Wechselwirkung auf der Nanoskala aus verschiedenen Perspektiven vorgestellt. Jedes Kapitel enthält eine kurze Einleitung, einen Theorieteil, Messdaten oder Simulationsergebnisse sowie eine Analyse; vervollständigt durch einen Schlussteil.
Die zentrale Arbeit an einer metallischen Metaoberfläche aus elliptischen Goldscheiben wird in Kapitel 3 vorgestellt. Der zugehörige Theorieteil führt in das Konzept von Oberflächen-Plasmon-Polaritonen (SPP) ein, das für den Forschungsbereich der Plasmonik im Allgemeinen wesentlich ist. Verschiedene Methoden zur Berechnung der Dispersionsrelation dieser Oberflächenmoden an ein- und mehrschichtigen Grenzflächen werden auf die untersuchte Metaoberflächenprobe angewendet. Das Modell sagt drei verschiedene Moden voraus, die sich an der Grenzfläche ausbreiten. Eine teil-gebundene ins Substrat abstrahlende Oberflächenmode sowie zwei vergrabene stark gebundene anisotrope Moden. Eine auf der Probe platzierte Nanokugel aus Silizium wird als radiale Anregungsquelle verwendet.
Der Vergleich mit s-SNOM-Nahfeldbildern zeigt, dass nur die schwach gebundene geführte Modenresonanz ausreichend angeregt wurde, um durch s-SNOM-Bildgebung nachgewiesen werden zu können. Die schwache Oberflächenbindung erklärt die scheinbar isotrope Ausbreitung auf der anisotropen Oberfläche. Die Beobachtung der verbleibenden stark eingegrenzten anisotropen vergrabenen Moden würde eine verbesserte tiefenempfindliche Auflösung des Systems erfordern, die im Prinzip für Schichtdicken von 20 nm möglich sein sollte. Darüber hinaus wirft die Beobachtung die Frage auf, ob die durch Impuls- und Modenvolumenanpassung der Nanokugel gegebene Anregungseffizienz einen ausreichenden Anregungsquerschnitt erzeugt, um nachweisbare vergrabene SPP-Moden zu erzeugen.
In Kapitel 4 wird die Idee der Visualisierung vergrabener elektrischer Felder mit s-SNOM fortgesetzt. Hier wird es auf die Untersuchung von WS_2 angewendet, einem zweidimensionalen TMDC-Material, welches Photolumineszenz zeigt. Durch die Strukturierung des Galliumphosphid-Substrats unter der hängenden Monolage, die von einer dünnen Schicht aus hBN getragen wird, wird die Photolumineszenzausbeute um den Faktor 10 erhöht. Dies wird durch den Entwurf einer lateralen DBR-Mikrokavität mit zusätzlich optimierter vertikaler Tiefe erreicht, die in das Substrat geätzt wurde.
Die hochauflösende Abbildung der elektrischen Feldverteilung im Resonator wird durch den Einsatz von s-SNOM ermöglicht, um die Verbesserung der Einkopplung durch diese beiden Ansätze zu bewerten. Es konnte festgestellt werden, dass die laterale Struktur überwiegend zur verstärkten Photolumineszenzausbeute beiträgt, während für die Einkopplung keine offensichtliche Verstärkung auf die vertikale Strukturoptimierung zurückgeführt werden konnte.
Das zweidimensionale Material WS_2 wird in Kapitel 5 erneut mit Hilfe von c-AFM untersucht. Unterschiedlich dicke Multilagen auf Graphen und Gold dienen als Tunnelbarrieren für vertikale Ströme zwischen Substrat und leitender c-AFM-Messpitze. Die Daten können mit einem Fowler-Nordheim-Modell mit Parametern für die Tunnelbreite und Schottky-Barrierenhöhen der beiden Grenzflächen erklärt werden. Die Messungen zeigen jedoch eine schwache Reproduzierbarkeit, was eine detailliertere Zusammenfassung der relevanten Fehlerquellen erfordert. In der Schlussfolgerung des Kapitels werden mehrere Schlüsselaspekte vorgeschlagen, die bei künftigen Messungen berücksichtigt werden sollten. Entscheidend ist, dass c-AFM sehr empfindlich auf die Adsorption von Wasserfilmen an der Probenoberfläche reagiert, worunter WS_2-Oberflächen unter Umgebungsbedingungen leiden...
We investigated the excitation of surface plasmon polaritons on gold films with the metallized probe tip of a scattering-type scanning near-field optical microscope (s-SNOM). The emission of the polaritons from the tip, illuminated by near-infrared laser radiation, was found to be anisotropic and not circularly symmetric as expected on the basis of literature data. We furthermore identified an additional excitation channel via light that was reflected off the tip and excited the plasmon polaritons at the edge of the metal film. Our results, while obtained for a non-rotationally-symmetric type of probe tip and thus specific for this situation, indicate that when an s-SNOM is employed for the investigation of plasmonic structures, the unintentional excitation of surface waves and anisotropic surface wave propagation must be considered in order to correctly interpret the signatures of plasmon polariton generation and propagation.
A new experimental system has been set up with the ability to investigate catalytic processes and charge transfer of acrylonitrile on copper. For this purpose a new Time of Flight Mass Spectrometer to measure both the reaction outcome and electron energy distributions has been designed and tested. First experiments have been carried out, in which the width of the two-photon photoelectron energy distribution can be varied by changing the wavelength of the incident laser beam. This method allows high precision measurements of the work function and will be useful in the study with adsorbates, physi- or chemisorbed. In first adsorption measurements the excitation of vibrational modes of acrylonitrile has been seen to be consistent with earlier gas-phase experiments. Electron energy spectra taken with the electron analyzer with high resolution showed a clear defect in the electron yield at energies around the energy of one vibrational mode, indicating the possibility of resonant vibrational excitation by electron impact. More indications to that process were found i first electron spectra from the new TOF-MS, since a threshold for the capture probability is found at energies close to vibrational excitation. The threshold vanishes when the exposure is amplified significantly, indicating that electrons are scattered multiple and no resonance are be observed anymore. The experiments carried out were just the starting point in understanding the mechanism of the reaction. A new femtosecond laser system which is currently set up will give not only a time-resolved information on the reaction pathways but also give the possibility to create non-thermal electrons and to study intermediate states of the photoemission and the influence of the adsorbate on them. In addition the rotation of the electron analyzer will permit angle-resolved measurements of the scattering process of the electrons and the vibrational excitation via this pathway. With the new cooling system applied it will also be interesting to study the excitation process at lower temperatures. Below -160° C there are different geometries of the molecule predicted to be present at the surface. At these temperatures the thermal effects should play a major role, so that a thermal decoupling of the electrons is very desirable.
Untersuchung von Korrelationseffekten in der Doppelphotoemission von normal- und supraleitendem Blei
(2012)
Im Rahmen dieser Arbeit wurde für die erstmalige Untersuchung der Doppelphotoemission von supraleitenden Materialien eine neue Messapparatur aufgebaut. Mit ihr lassen sich auf eine neue Weise Korrelationseffekte zwischen zwei Elektronen untersuchen, denn beide werden für jedes Reaktionsereignis mit ihrem vollständigen Impulsvektor aufgezeichnet. Die Apparatur kann daher für einen direkten Nachweis der Cooperpaarung in Supraleitern verwendet werden. Dazu wurden ein speziell für diesen Zweck angepasstes Spektrometer, Vakuumsystem und Probenhalter konstruiert. Ein mehrfach verbessertes Vakuumsystem sorgte dafür, dass eine Bleioberfläche über einen Zeitraum von mindestens 15 Stunden nach einer Reinigung gemessen werden konnte. Das Spektrometer erlaubte die koinzidente Messung von Elektronen über einen großen Raumwinkelbereich mit ausschließlich elektrischen Feldern. Dadurch war es auch im supraleitenden Zustand möglich, die Trajektorien der Elektronen zu berechnen. Die Energieauflösung für jedes Elektron lag zwischen 1/30 und 1/50, je nach untersuchtem Emissionswinkel. Ein eigens entwickelter Probenhalter erlaubte es, eine nur von einer Seite thermisch abgeschirmte Probe auf eine Temperatur von 4,5 K zu kühlen. Die Experimente wurden an einer Beamline des Berliner Synchrotrons BESSY durchgeführt.
Von entscheidender Bedeutung für die Auswertung der Daten ist die Qualität der Pulserkennungsroutine. Sie bestimmt die Totzeit der Messapparatur, das heisst wie nahe zwei Elektronen zeitlich und räumlich beieinander liegen dürfen, um noch detektiert zu werden. Sie beeinflusst somit die Beobachtung erheblich. In den als digitalisierte Pulse aufgenommen Rohdaten besteht die Schwierigkeit darin, zwei übereinander liegende Signale als solche zu erkennen und die richtige Zeit beider Signale zu bestimmten. Dies wurde erheblich verbessert, indem ein in Vorabeiten simulierter Doppelpulsalgorithmus modifiziert und erstmalig verwendet wurde. In der Folge konnte die Totzeit deutlich verringert und daher bis zu 20% mehr Doppelereignisse gefunden werden. Darüber hinaus ließen sich Fehler bei der Zeiterkennung nahe aufeinander folgender Pulse korrigieren. Ein in diesem Zusammenhang entwickeltes Programm erzeugte durch die Addition von gemessenen Einzelpulsen künstliche Doppelereignisse mit beliebiger Abstandsverteilung und erlaubte so erstmals eine exakte Simulation der Detektortotzeit mit verschiedenen Pulserkennungsalgorithmen.
Neben den Koinzidenzereignissen wurden auch die Ergebnisse der gewöhnlichen Photoemission untersucht und mit Bandstrukturrechnungen verglichen. Aufgrund der Messmethode wurde keine Vorauswahl bezüglich des Emissionswinkels oder der kinetischen Energie getroffen. Die Ergebnisse der Fermiflächen stimmen innerhalb der erreichten Auflösung mit den theoretischen Vorhersagen überein. Ebenso konnten die Strukturen in den Parallelimpulsspektren der Elektronen, die aus lokalisierten Energieniveaus emittiert wurden, mit der Interferenz der ausgehenden Wellenfunktionen erklärt werden. Eine Simulation dieses Effekts lieferte trotz der vergleichsweise sehr niedrigen Elektronenenergien eine gute Übereinstimmung der wesentlichen Merkmale.
Es wurden Doppelphotoemissionspektren von Blei bei verschiedenen Photonenenergien im Bereich von 21,22 eV bis 40 aufgenommen. Dabei konnten verschiedene Emissionskanäle identifiziert werden. Das Korrelationsloch ist ein sehr grundlegender Effekt, der aufgrund der Coulombabstoßung und des Pauli-Prinzips auftritt und daher bei allen Metallen vorkommt. Betrachtet man das Korrelationsloch im Impulsraum, so führt es dazu, dass zwei gleichzeitig emittierte Elektronen keine ähnlichen Impulsvektoren besitzen dürfen. Durch die verbesserten Pulserkennungsalgorithmen war es möglich, das Korrelationsloch zu untersuchen und über einen weiten Energiebereich zu vermessen. Es zeigte sich wie erwartet als Verarmungszone in der Impulsverteilung eines Elektrons um den Impuls eines zweiten. Ein solcher Effekt ist mit einem einzelnen Detektor sehr schwer zu messen, da die Totzeit die gleiche Auswirkung auf die Spektren hat. Durch eine Simulation konnte ihr Einfluss in jedem Spektrum herausgefunden und so beide Effekte voneinander getrennt werden. Sie stehen damit für einen Vergleich mit einer noch zu entwickelnden theoretischen Vorhersage zur Verfügung.
Aufgrund der bei Blei sehr nahe an der Fermikante liegenden, lokalisierten Energieniveaus konnte der Augerzerfall aus dem Valenzband identifiziert und untersucht werden. Korrelationseffekte zwischen den beiden Elektronen spielten aufgrund des sehr breiten Valenzbandes wie erwartet eine untergeordnete Rolle. Dies ließ sich nachweisen, indem die Energieverteilung durch eine Selbstfaltung der Valenzbandzustandsdichte beschrieben wurde und die Winkelverteilung der Augerelektronen keine Beeinflussung durch die Emissionsrichtung der Photoelektronen zeigte. Beide Beobachtungen deuten auf einen vollständig unabhängigen Emissionsprozess der beiden Elektronen hin. Überraschenderweise zeigte sich aber eine Energieverschiebung des Photoelektrons, abhängig von der kinetischen Energie des Augerelektrons. Dieser in der Gasphase als Post-Collision-Interaction bekannte Effekt sollte aufgrund der schnellen Abschirmung der im Festkörper zurückbleibenden Löcher nicht auftauchen. Die Ursache für die Energieverschiebung ist noch unbekannt.
Für die Identifizierung der Emission von Cooperpaaren wurden Messungen oberhalb und unterhalb der Sprungtemperatur bei verschiedenen Photonenenergien zwischen 20 eV und 40 eV durchgeführt. Verschiedene Spektren wurde nach der Signatur des Prozesses untersucht. Aufgrund der geringen Statistik konnte er nicht identifiziert werden. Demnach konnte auch die theoretische Vorhersage nicht widerlegt werden. Da dieses Experiment aus technischer Sicht äußerst herausfordernd ist, war die Untersuchung von Blei, als einfach zu präparierendes Material mit hoher Sprungtemperatur, naheliegend. Es stellte sich jedoch durch die Auswertung heraus, dass es im Hinblick auf die untersuchte Fragestellung einen wesentlichen Nachteil besitzt. Die Hauptintensität befindet sich im Gegensatz zu Kupfer für alle hier verwendeten Photonenenergien bei niedrigen Elektronenenergien, so dass nur wenige Ereignisse in dem für die Cooperpaaremission interessanten Energiefenster liegen.
We have studied one-proton-removal reactions of about 500MeV/u 17Ne beams on a carbon target at the R3B/LAND setup at GSI by detecting beam-like 15O-p and determining their relative-energy distribution. We exclusively selected the removal of a 17Ne halo proton, and the Glauber-model analysis of the 16F momentum distribution resulted in an s2 contribution in the 17Ne ground state of about 40%.
A synchrotron is a particular type of cyclic particle accelerator and the first accelerator concept to enable the construction of large-scale facilities [10], such as the largest particle accelerator in the world, the 27-kilometre-circumference Large Hadron Collider (LHC) by CERN near Geneva, Switzerland, the European Synchrotron Radiation Facility (ESRF) in Grenoble, France for the synchrotron radiation, the superconducting, heavy ion synchrotron SIS100 under construction for the FAIR facility at GSI, Darmstadt, Germany and so on. Unlike a cyclotron, which can accelerate particles starting at low kinetic energy, a synchrotron needs a pre-acceleration facility to accelerate particles to an appropriate initial value before synchrotron injection. A pre-acceleration can be realized by a chain of other accelerator structures like a linac, a microtron in case of electrons, for example, Proton and ion injectors Linac 4 and Linac 3 for the LHC, UNLAC as the injector for the SIS18 in GSI and in future the SIS18 as injector for the SIS100. The linac is a commonly used injector for the ion synchrotron and consists of some key components. The three main parts of a linac are: An ion source creating the particles, a buncher system or an RFQ followed by the main drift tube accelerator DTL. In order to meet the energy and the beam current requirement of a synchrotron injector linac, its cost is a remarkable percentage of the total facility costs.
However, the normal conducting linac operation at cryogenic temperatures can be a promising solution in improving the efficiency and reducing the costs of a linac. Synchrotron injectors operate at very low duty factor with beam pulse lengths in 1 micros to 100 micros range, as most of the time is needed to perform the synchrotron cycle. Superconducting linacs are not convenient, as they cannot efficiently operate at low duty factor and high beam currents.
The cryogenic operation of ion linacs is discussed and investigated at IAP in Frankfurt since around 2012 [1, 37]. The motivation was to develop very compact synchrotron injectors at reduced overall linac costs per MV of acceleration voltage. As the needed beam currents for new facilities are increasing as well, the new technology will also allow an efficient realization of higher injector linac energies, which is needed in that case. Operating normal conducting structures at cryogenic temperature exploits the significantly higher conductivity of copper at temperatures of liquid nitrogen and below. On the other hand, the anomalous skin effect reduces the gain in shunt impedance quite a bit[25, 31, 9]. Some intense studies and experiments were performed recently, which are encouraging with respect to increased field levels at linac operation temperatures between 30 K and 70 K [17, 24, 4, 23, 5, 8]. While these studies are motivated by applications in electron acceleration at GHz-frequencies, the aim of this paper is to find applications in the 100 to 700 MHz range, typical for proton and ion acceleration. At these frequencies, a higher impact in saving RF power is expected due to the larger skin depth, which is proportional to the frequency to the power of negative half with respect to the normal skin effect. On the other hand, it is assumed that the improvement in maximum surface field levels will be similar to what was demonstrated already for electron accelerator cavities. This should allow to find a good compromise between reduced RF power needs for achieving a given accelerator voltage and a reduced total linac length to save building costs.
A very important point is the temperature stability of the cavity surface during the RF pulse. This is of increasing importance the lower the operating temperature is chosen: the temperature dependence of the electric conductivity in copper gets rather strong below 80 K, as long as the RRR - value of the copper is adequate. It is very clear, that this technology is suited for low duty cycle operated cavities only - with RF pulse lengths below one millisecond. At longer pulses the cavity surface will be heated within the pulse to temperatures, where the conductivity advantage is reduced substantially. These conditions fit very well to synchrotron injectors or to pulsed beam power applications.
H – Mode structures of the IH – and of the CH – type are well-known to have rather small cavity diameters at a given operating frequency. Moreover, they can achieve effective acceleration voltage gains above 10 MV/m even at low beam energies, and already at room temperature operation[29]. With the new techniques of 3d – printing of stainless steel and copper components one can reduce cavity sizes even further – making the realization of complex cooling channels much easier.
Another topic are copper components in superconducting cavities – like power couplers. It is of great importance to know exactly the thermal losses at these surfaces, which can’t be cooled efficiently in an easy way.
This work is focused on the anomalous skin effect in copper and how it affects the efficiency of copper-cavities in the temperature range 40-50 K. The quality factor Q of three coaxial cavities was measured over the temperature range from 10 K to room temperature in the experiment. The three coaxial cavities have the same structure, but different lengths, which correspond to resonant frequencies: around 100 MHz, 220 MHz and 340 MHz. Furthermore, the effects of copper-plating and additional baking in the vacuum oven on the quality factor Q are studied in the experiment. The motivation is to check the feasibility of an efficient, pulsed, ion linac, operated at cryogenic temperatures.
Measurement of iodine species and sulfuric acid using bromide chemical ionization mass spectrometers
(2021)
Iodine species are important in the marine atmosphere for oxidation and new-particle formation. Understanding iodine chemistry and iodine new-particle formation requires high time resolution, high sensitivity, and simultaneous measurements of many iodine species. Here, we describe the application of a bromide chemical ionization mass spectrometer (Br-CIMS) to this task. During the iodine oxidation experiments in the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber, we have measured gas-phase iodine species and sulfuric acid using two Br-CIMS, one coupled to a Multi-scheme chemical IONization inlet (Br-MION-CIMS) and the other to a Filter Inlet for Gasses and AEROsols inlet (Br-FIGAERO-CIMS). From offline calibrations and intercomparisons with other instruments, we have quantified the sensitivities of the Br-MION-CIMS to HOI, I2, and H2SO4 and obtained detection limits of 5.8 × 106, 3.8 × 105, and 2.0 × 105 molec. cm−3, respectively, for a 2 min integration time. From binding energy calculations, we estimate the detection limit for HIO3 to be 1.2 × 105 molec. cm−3, based on an assumption of maximum sensitivity. Detection limits in the Br-FIGAERO-CIMS are around 1 order of magnitude higher than those in the Br-MION-CIMS; for example, the detection limits for HOI and HIO3 are 3.3 × 107 and 5.1 × 106 molec. cm−3, respectively. Our comparisons of the performance of the MION inlet and the FIGAERO inlet show that bromide chemical ionization mass spectrometers using either atmospheric pressure or reduced pressure interfaces are well-matched to measuring iodine species and sulfuric acid in marine environments.
In our daily life, we carry out lots of tasks like typing, playing tennis, and playing the piano, without even noticing there is sequence learning involved. No matter how simple or complex they are, these tasks require the sequential planning and execution of a series of movements. As an ability of primary importance in one’s life, and an ability that everyone manages to learn, action-sequence learning has been studied by researchers from different fields: psychologists, neurophysiologists as well as roboticists. In the concept of sequence learning, perceptual learning and motor learning, implicit and explicit learning have been studied and discussed independently.
We are interested in infancy research, because infants, with underdeveloped brain functions and with limited motor ability, have little experience with the world and not yet built internal models as presumption of how to interpret the world. A series of infant experiments in the 1980s provided evidence that infants can rapidly develop anticipatory eye movements for visual events. Even when infants have no control of those spatial-temporal patterns, they can respond actually prior to the onset of the visual event, referred as "Anticipation".
In this work, we applied a gaze-contingent paradigm using real-time eye tracking to put 6- and 8-month-old infants in direct control of their visual surroundings. This paradigm allows the infant to change an image on a screen by looking at a peripheral red disc, which functions as a switch. We found that infants quickly learn to perform eye movements to trigger the appearance of new stimuli and that they anticipate the consequences of their actions in an early stage of the experiment.
Attention-shift from learning one stimulus to the next novel stimulus is important in sequence learning. In the test phase of infant visual habituation with two objects, we propose a new theory of explaining the familiarity-to-novelty shift. In our opinion an infant’s interest in a stimulus is related to its learning progress, the improvement of performance. As a consequence, infants prefer the stimulus which their current learning progress is maximal for, naturally giving rise to a familiarity-to-novelty shift in certain situations. Our network model predicts that the familiarity-to-novelty-shift only emerges for complex stimuli that produce bell-shaped learning curves after brief familiarization, but does not emerge for simple stimuli that produce exponentially decreasing learning curves or for long familiarization time, which is consistent with experimental results. This research suggests the infant's interest in a stimulus may be related to its current learning progress. This can give rise to a dynamic familiarity-to-novelty shift depending on both the infant's learning efficiency and the task complexity.
We know that for both infants and adults, the performance on certain motor-sequence tasks can be improved through practice. However, adults usually have to perform complex tasks in complicated environments; for example, learning multiple tasks is unavoidable in our daily life. In existing research, learning multiple tasks showed puzzling and seemingly contradictory results. On the one hand, a wide variety of proactive and retroactive interference effects have been observed when multiple tasks have to be learned. On the other hand, some studies have reported facilitation and transfer of learning between different tasks.
In order to find out the interaction between multiple-task learning, and to find an optimal training schedule, we use a recurrent neural network to model a series of experiments on movement sequence learning. The network model learns to carry out the correct movement sequences through training and reproduces differences between training schedules such as blocked training vs. random training in psychophysics experiments. The network model also shows striking similarity to human performance, and makes prediction for tasks similarity and different training schedules.
In conclusion, the thesis presents learning sequences of actions in infants and recurrent neural networks. We carried out a gaze-contingent experiment to study infants’ rapid anticipation of their own action outcomes, and we also constructed two recurrent neural network models, with one model explaining infant attention shift in visual habituation, and the other model directing to task similarity and training schedule in motor sequence control in adults.
By using the background field method of QCD in a path integral approach, we derive the equation of motion for the classical chromofield and for the gluon in a system containing the gluon and the classical chromofield simul- taneously. This inhomogeneous field equation contains a current term, which is the expectation value of a composite operator including linear, square and cubic terms of the gluon field. We also derive identities which the current should obey from the gauge invariance. We calculate the current at the leading order where the current induced by the gluon is opposite in sign to that induced by the quark. This is just the feature of the non-Abelian gauge field theory which has asymptotic freedom. Physically, the induced current can be treated as the displacement current in the polarized vacuum, and its e ect is equivalent to redefining the field and the coupling constant. PACS: 12.38.-t,12.38.Aw,11.15.-q,12.38.Mh
The non-equilibrium quantum field dynamics is usually described in the closed-time-path formalism. The initial state correlations are introduced into the generating functional by non-local source terms. We propose a functional approach to the Dyson-Schwinger equation, which treats the non-local and local source terms in the same way. In this approach, the generating functional is formulated for the connected Green functions and one-particle-irreducible vertices. The great advantages of our approach over the widely used two-particle-irreducible method are that it is much simpler and that it is easy to implement the procedure in a computer program to automatically generate the Feynman diagrams for a given process. The method is then applied to a pure gluon plasma to derive the gauge-covariant transport equation from the Dyson-Schwinger equation in the background covariant gauge. We discuss the structure of the kinetic equation and show its relationship with the classical one. We derive the gauge-covariant collision part and present an approximation in the vicinity of equilibrium. The role of the non-local source kernel in the non-equilibrium system is discussed in the context of a free scalar field. PACS numbers: 12.38.Mh, 25.75.-q, 24.85.+p, 11.15.Kc
We derive the kinetic equation for pure gluon QCD plasma in a general way, applying the background field method. We show that the quantum kinetic equation contains a term as in the classical case, that describes a color charge precession of partons moving in the gauge field. We emphasize that this new term is necessary for the gauge covariance of the resulting equation.
We derive the quantum kinetic equation for a pure gluon plasma, applying the background field and closed-time-path method. The derivation is more general and transparent than earlier works. A term in the equation is found which, as in the classical case, corresponds to the color charge precession for partons moving in the gauge field. PACS numbers: 12.38.Mh, 25.75.-q, 24.85.+p, 11.15.Kc
We present a new type of flow analysis, based on a particle-pair correlation function, in which there is no need for an event-by-event determination of the reaction plane. Consequently, the need to correct for dispersion in an estimated reaction plane does not arise. Our method also offers the option to avoid any influence from particle misidentification. Using this method, streamer chamber data for collisions of Ar+KCl and Ar+BaI2 at 1.2 GeV/nucleon are compared with predictions of a nuclear transport model.
A deep convolutional neural network (CNN) is developed to study symmetry energy (Esym(ρ)) effects by learning the mapping between the symmetry energy and the two-dimensional (transverse momentum and rapidity) distributions of protons and neutrons in heavy-ion collisions. Supervised training is performed with labeled data-set from the ultrarelativistic quantum molecular dynamics (UrQMD) model simulation. It is found that, by using proton spectra on event-by-event basis as input, the accuracy for classifying the soft and stiff Esym(ρ) is about 60% due to large event-by-event fluctuations, while by setting event-summed proton spectra as input, the classification accuracy increases to 98%. The accuracies for 5-label (5 different Esym(ρ)) classification task are about 58% and 72% by using proton and neutron spectra, respectively. For the regression task, the mean absolute errors (MAE) which measure the average magnitude of the absolute differences between the predicted and actual L (the slope parameter of Esym(ρ)) are about 20.4 and 14.8 MeV by using proton and neutron spectra, respectively. Fingerprints of the density-dependent nuclear symmetry energy on the transverse momentum and rapidity distributions of protons and neutrons can be identified by convolutional neural network algorithm.
Complex I couples the free energy released from quinone (Q) reduction to pump protons across the biological membrane in the respiratory chains of mitochondria and many bacteria. The Q reduction site is separated by a large distance from the proton-pumping membrane domain. To address the molecular mechanism of this long-range proton-electron coupling, we perform here full atomistic molecular dynamics simulations, free energy calculations, and continuum electrostatics calculations on complex I from Thermus thermophilus. We show that the dynamics of Q is redox-state-dependent, and that quinol, QH2, moves out of its reduction site and into a site in the Q tunnel that is occupied by a Q analog in a crystal structure of Yarrowia lipolytica. We also identify a second Q-binding site near the opening of the Q tunnel in the membrane domain, where the Q headgroup forms strong interactions with a cluster of aromatic and charged residues, while the Q tail resides in the lipid membrane. We estimate the effective diffusion coefficient of Q in the tunnel, and in turn the characteristic time for Q to reach the active site and for QH2 to escape to the membrane. Our simulations show that Q moves along the Q tunnel in a redox-state-dependent manner, with distinct binding sites formed by conserved residue clusters. The motion of Q to these binding sites is proposed to be coupled to the proton-pumping machinery in complex I.
Formation of Hubbard-like bands as a fingerprint of strong electron-electron interactions in FeSe
(2017)
We use angle-resolved photo-emission spectroscopy (ARPES) to explore the electronic structure of single crystals of FeSe over a wide range of binding energies and study the effects of strong electron-electron correlations. We provide evidence for the existence of "Hubbard-like bands" at high binding energies consisting of incoherent many-body excitations originating from Fe 3d states in addition to the renormalized quasiparticle bands near the Fermi level. Many high energy features of the observed ARPES data can be accounted for when incorporating effects of strong local Coulomb interactions in calculations of the spectral function via dynamical mean-field theory, including the formation of a Hubbard-like band. This shows that over the energy scale of several eV, local correlations arising from the on-site Coulomb repulsion and Hund's coupling are essential for a proper understanding of the electronic structure of FeSe and other related iron based superconductors.
We calculate p, ±,K± and (+ 0) rapidity distributions and compare to experimental data from SIS to SPS energies within the UrQMD and HSD transport approaches that are both based on string, quark, diquark (q, ¯q, qq, ¯q ¯q) and hadronic degrees of freedom. The two transport models do not include any explicit phase transition to a quark-gluon plasma (QGP). It is found that both approaches agree rather well with each other and with the experimental rapidity distributions for protons, s, ± and K±. In- spite of this apparent agreement both transport models fail to reproduce the maximum in the excitation function for the ratio K+/ + found experimen- tally between 11 and 40 A·GeV. A comparison to the various experimental data shows that this failure is dominantly due to an insu cient description of pion rapidity distributions rather than missing strangeness . The modest di erences in the transport model results on the other hand can be attributed to di erent implementations of string formation and frag- mentation, that are not su ciently controlled by experimental data for the elementary reactions in vacuum.