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Predictive Place-Cell Sequences for Goal-Finding Emerge from Goal Memory and the Cognitive Map: A Computational Model
Get PDFHippocampal place-cell sequences observed during awake immobility often represent previous experience, suggesting a role in memory processes. However, recent reports of goals being overrepresented in sequential activity suggest a role in short-term planning, although a detailed understanding of the origins of hippocampal sequential activity and of its functional role is still lacking. In particular, it is unknown which mechanism could support efficient planning by generating place-cell sequences biased toward known goal locations, in an adaptive and constructive fashion. To address these questions, we propose a model of spatial learning and sequence generation as interdependent processes, integrating cortical contextual coding, synaptic plasticity and neuromodulatory mechanisms into a map-based approach. Following goal learning, sequential activity emerges from continuous attractor network dynamics biased by goal memory inputs. We apply Bayesian decoding on the resulting spike trains, allowing a direct comparison with experimental data. Simulations show that this model (1) explains the generation of never-experienced sequence trajectories in familiar environments, without requiring virtual self-motion signals, (2) accounts for the bias in place-cell sequences toward goal locations, (3) highlights their utility in flexible route planning, and (4) provides specific testable predictions
Hängefördersystem mit Trag- und Gleitelement aus Wood Plastic Composite (WPC)
Get PDFErneuerbare Werkstoffe (z.B. WPC) können metallische substituieren, indem eine Kombination aus technischen, wirtschaftlichen und ökologischen Vorteilen in Bauweise und Bauteilen in der Intralogistik Anwendung finden. Vorgestellt werden die wichtigsten Schritte zur Entwicklung eines Hängefördersystems mit einem Trag- und Gleitprofil aus WPC. Schwerpunkte sind die Verbindungsstellen, die Kurvensegmente und die Weiche. Es erfolgt eine Beurteilung der Gebrauchstauglichkeit des Gesamtsystems
Detachable Connection for Thin Homogeneous Conveyor Belts in the Food Industry
No full textBelt conveyor systems play an important role in many areas of industrial production. Thereby, the transport of foods demands special requirements and restrictions to avoid contamination and microbial growth. The belts used here are often manufactured as yard goods for technical production reasons. After cutting these belts to length, it is necessary to join the ends together. To guarantee assembly, the belts are among other things equipped with detachable connections. Accordingly, this article deals with the development of new detachable connection for thin unreinforced conveyor belts in the food industry. Besides reduction of critical areas (undercuts, breakthroughs …) which favor the accumulation of bacteria additional focuses are the increase of tensile strength as well as a simple and fast assembly and disassembly of the belt to ensure cleaning and disinfection. Moreover, effective and economic production technologies should be applied.Bandförderer spielen in vielen Industriebereichen eine wichtige Rolle. Der Transport von Lebensmitteln stellt dabei aufgrund von Verschmutzung und Mikrobenbildung besondere Anforderungen und Restriktionen an das Fördersystem. Hier verwendete lebensmittelkonforme Bänder werden aus fertigungstechnischen Gründen oft als Meterware produziert, im Anschluss auf Länge geschnitten und die Enden verbunden. Um die Montage zu gewährleisten kommen dazu unter anderem lösbare Bandverbindungen zum Einsatz. Der Beitrag befasst sich entsprechend mit der Entwicklung einer neuen lösbaren Verbindung für dünne, unverstärkte Förderbänder in der Lebensmittelindustrie. Neben der Reduzierung von kritischen Bereichen wie Hinterschnitten und Durchbrüchen liegen weitere Augenmerke auf der Erhöhung der Zugfestigkeit, sowie einer einfachen und schnellen Montage bzw. Demontage der Verbindung zu Reinigungszwecken. Zudem soll eine wirtschaftliche Fertigung gewährleistet werden
Dynamic Studies on a Slide Chain Conveyor System
Get PDFIn slide chain conveyors vibrations often appear. These cause detrimental effects in conveying process and decrease the durability of chains. To study the vibrations, a multi-body simulation model has been developed, in which rheological elements are used to represent the dynamic effects. A focus was determining material values required for the model. These were identified by hysteresis experiments. Finally, the model was verified by comparing simulation results with measurements in the conveyor system.In Gleitkettenfördersystemen werden häufig Schwingungen der Kette beobachtet, die einen zuverlässigen Förderprozess auf diesen Anlagen beeinträchtigen können. Ziel dieser Arbeit ist die Erforschung dieser Schwingungen mit Hilfe von einem Mehrkörpersimulationsmodell. Zur Abbildung der dynamischen Effekte wurden rheologische Elemente verwendet. Ein Schwerpunkt lag bei der Ermittlung der für das Modell notwendigen Materialkennwerte. Diese wurden mit Hilfe von Hystereseversuchen herausgefunden. Zum Schluss wurde das Modell über einen Abgleich zwischen Simulation und Messung im Fördersystem verifiziert
Stochastic Fluctuations in Endoreversible Systems
Get PDFIn dieser Arbeit wird erstmalig der Einfluss stochastischer Schwankungen auf endoreversible Modelle untersucht. Hierfür wird die Novikov-Maschine mit drei verschieden Wärmetransportgesetzen (Newton, Fourier, asymmetrisch) betrachtet. Während die maximale verrichtete Arbeit und der dazugehörige Wirkungsgrad recht einfach im Falle konstanter Wärmebadtemperaturen hergeleitet werden können, ändern sich dies, falls die Temperaturen stochastisch fluktuieren können. Im letzteren Fall muss die stochastische optimale Kontrolltheorie genutzt werden, um das Maximum der zu erwartenden Arbeit und die dazugehörige Kontrollstrategie zu ermitteln. Im Allgemeinen kann die Lösung derartiger Probleme auf eine nichtlineare, partielle Differentialgleichung, welche an eine Optimierung gekoppelt ist, zurückgeführt werden. Diese Gleichung wird stochastische Hamilton-Jacobi-Bellman-Gleichung genannt. Allerdings können, wie in dieser Arbeit dargestellt, die Berechnungen vereinfacht werden, wenn man annimmt, dass die Fluktuationen unabhängig von der betrachteten Kontrollvariablen sind. In diesem Fall zeigen analytische Betrachtungen, dass die Gleichungen für die verrichtete Arbeit and den Wirkungsgrad ihre ursprüngliche Form behalten, aber manche Terme müssen durch entsprechende Zeitmittel bzw. Erwartungswerte ersetzt werden, jeweils abhängig von der betrachteten Art der Kontrolle. Basierend auf einer Analyse der Leistungsparameter im Falle einer Gleichverteilung der heißen Temperatur der Novikov-Maschine können Schlussfolgerungen auf deren Monotonieverhalten gezogen werden. Der Vergleich verschiedener, zeitunabhängiger, symmetrischer Verteilungen führt zu einer bis dato unbekannten Erweiterung des Curzon-Ahlborn-Wirkungsgrades im Falle kleiner Schwankungen. Weiterhin wird eine Analyse einer Novikov-Maschine mit asymmetrischen Wärmetransport, bei der das Verhalten der heißen Temperatur durch einen Ornstein-Uhlenbeck-Prozess beschrieben wird, durchgeführt. Abschließend wird eine Novikov-Maschine mit Fourierscher Wärmeleitung, bei der die Dynamik der heißen Temperatur von der Kontrollvariable abhängt, betrachtet. Durch das Lösen der Hamilton-Jacobi-Bellman-Gleichung können neuartige Schlussfolgerungen gezogen werden, wie derartige Systeme optimal zu steuern sind.In this thesis, the influence of stochastic fluctuations on the performance of endoreversible engines is investigated for the first time. For this, a Novikov-engine with three different heat transport laws (Newtonian, Fourier, asymmetric) is considered. While the maximum work output and corresponding efficiency can be deduced easily in the case of constant heat bath temperatures, this changes, if these temperatures are allowed to fluctuate stochastically. In the latter case, stochastic optimal control theory has to be used to find the maximum of the expected work output and the corresponding control policy. In general, solving such problems leads to a non-linear, partial differential equation coupled to an optimization, called the stochastic Hamilton-Jacobi-Bellman equation. However, as presented in this thesis, calculations can be simplified, if one assumes that the fluctuations are independent of the considered control variable. In this case, analytic considerations show that the equations for performance measures like work output and efficiency keep their original form, but terms have to be replaced by appropriate time averages and expectation values, depending on the considered control type. Based on an analysis of the performance measures in the case of a uniform distribution of the hot temperature of the Novikov engine, conclusions on their monotonicity behavior are drawn. The comparison of several, time independent, symmetric distributions reveals a to date unknown extension to the Curzon-Ahlborn efficiency in the case of small fluctuations. Furthermore, an analysis of a Novikov engine with asymmetric heat transport, where the behavior of the hot temperature is described by an Ornstein-Uhlenbeck process, is performed. Finally, a Novikov engine with Fourier heat transport is considered, where the dynamics of the hot temperature depends on the control variable. By solving the corresponding Hamilton-Jacobi-Bellman equation, new conclusions how to optimally control such systems are drawn
Bis(β-diketonato)- and allyl-(β-diketonato)-palladium(II) complexes: synthesis, characterization and MOCVD application
Get PDFThe syntheses and characterization of the palladium complexes [Pd(accp)2] (7), [Pd(acch)2] (8), [Pd(η3-CH2CMeCH2)(accp)] (11), [Pd(η3-CH2CMeCH2)(acch)] (12), [Pd(η3-CH2CtBuCH2)(accp)] (13) and [Pd(η3-CH2CtBuCH2)(acch)] (14) (accp = 2-acetylcyclopentanoate; acch = 2-acetylcyclohexanoate) are reported. These complexes are available by the reaction of Haccp (2-acetylcyclopentanone) and Hacch (2-acetylcyclohexanone) with Na2[Pd2Cl6] forming 7 and 8 or with [(Pd(η3-CH2CRCH2)(μ-Cl))2] (9, R = Me; 10, R = tBu) forming 11–14. The molecular structures of 7, 8 and 14 are discussed. Complexes 7 and 8 consist of a square-planar coordinated Pd atom with two trans-positioned bidentate β-diketonate ligands. The asymmetric unit of 14 exhibits one molecule of the palladium complex and a half molecule of water. The thermal behavior of 7, 8 and 11–14 and their vapor pressure data were investigated to show, if the appropriate complexes are suited as CVD precursors for palladium layer formation. Thermogravimetric studies showed the evaporation of the complexes at atmospheric pressure upon heating. The vapor pressure of 7, 8 and 11–14 was measured by using thermogravimetric analysis, giving vapor pressure values ranging from 0.62 to 2.22 mbar at 80 °C. Chemical vapor deposition studies were carried out applying a vertical cold wall CVD reactor. Either oxygen or forming gas (N2/H2, ratio 90/10, v/v) was used as reactive gas. Substrate temperatures of 350 and 380 °C were utilized. With 11–14 dense and conformal as well as particulate palladium films were obtained, as directed by SEM studies, whereas 7 and 8 failed to give thin films, which is probably attributed to their high thermal stability in the gas phase. For all deposited layers, XPS measurements confirmed the partial oxidation of palladium to palladium(II) oxide at 380 °C, when oxygen was used as reactive gas. In contrast, thin layers of solely metallic palladium were obtained utilizing forming gas during the deposition experiments.Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
Roll-to-roll infrared and hot-air sintering of gravure-printed Ag layer based on in situ tension measuring and analysis
Get PDFThis study presents a method developed to achieve the roll-to-roll sintering of printed Ag patterns based on exposure to hot air, near-infrared, and mid-infrared sources. The sintering energy was quantified and evaluated based on theoretical and experimental calculations. Moreover, the effect of the sintering energy on the web tension was simultaneously considered.Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
Systemübergreifender Simulationsansatz zur Auslegung, Fertigung und Qualitätsicherung am Beispiel einer Bogenverzahnung
Get PDFDie Herstellung bogenverzahnter Bauteile für Antriebswellen ist durch einen hohen fertigungstechnischen Aufwand gekennzeichnet. Dieser erhöht sich mit zunehmender Komplexität der Verzahnungsgeometrie. Mit dem Beginn der Fertigung von Hochleistungsspindeln, stellt sich die Frage nach einer Alternative zur 5-Achsfräser Bearbeitung.
Der folgende Mathcad-Creo-Mechanismen Vortrag umfasst das herkömmliche Erstellen von Bogenverzahnungen und die Weiterentwicklung 5-Achsschleifen mittels Bahndatenberechnung, der Vermessung der Bauteile und gegebenenfalls Korrektur der Bearbeitung
Cognitive Investments in Academic Success: The Role of Need for Cognition at University
Get PDFPrevious research has shown that Need for Cognition (NFC), the individual tendency to engage in and enjoy cognitive endeavors, contributes to academic performance. Most studies on NFC and related constructs have thereby focused on grades to capture tertiary academic success. This study aimed at a more comprehensive approach on NFC’s meaning to success in university. We examined not only performance but also rather affective indicators of success. The current sample consisted of 396 students of different subjects with a mean age of 24 years (139 male). All participants took part in an online survey that assessed NFC together with school performance and further personality variables via self-report. Success in university was comprehensively operationalized including performance, satisfaction with one’s studies, and thoughts about quitting/changing one’s major as indicators. The value of NFC in predicting tertiary academic success was examined with correlation analyses and path analysis. NFC significantly correlated with all success variables with the highest correlation for study satisfaction. Path analysis confirmed the importance of NFC for study satisfaction showing that NFC had a significant direct effect on study satisfaction and via this variable also a significant indirect effect on termination thoughts. This study clearly indicates that NFC broadly contributes to the mastery of academic requirements and that it is worthwhile to intensify research on NFC in the context of tertiary education
Application of Laser Scanning as a Pre-machining metrology technique in Jet-ECM
Get PDFIn Electrochemical Machining (ECM), where the material removal takes place based on the anodic dissolution of the workpiece material, the working distance is one of the most important parameters. Especially in Jet Electrochemical Machining (Jet-ECM), where a micro nozzle is moved over the initial surface of the workpiece in order to apply an electrolytic free jet to produce the desired shapes, the distance between the nozzle and the workpiece becomes even more important. On the one hand a small working distance is aspired to achieve high current densities resulting in a high efficiency of the process. On the other hand the working distance needs to be large enough to avoid damages on the micro nozzle caused by electrical discharges or mechanical contact. Hence, the adjustment of the working gap is essential to realize a precise, effective and secure Jet-ECM process.
The control of the gap size is done based on the data gathered before machining by surface measurement. Until now, the initial surface has been detected by electrostatic probing through moving the nozzle stepwise to the work piece surface and detect the voltage drop between the nozzle and the work piece. With this strategy, only a limited number of points can be detected within adequate time. Hence, in most cases only three points of the initial surface are detected in order to adjust the working distance according to the planar inclination of the workpiece. The coordinates of the three detected points are used to calculate the normal vector of the initial surface. In recent studies, another strategy was analysed, which is realized by dividing the surface into smaller areas and respectively calculating the normal vector of each area in order to obtain more accurate data of the initial surface. A further strategy is to use probing along the machining path of the tool and to gather the coordinates of a number of points along the path.
The above mentioned methods usually do not ensure the precise control of the gap size especially for the surfaces with complex geometry with locally confined convex and concave shapes and are highly affected by the size of the probe. In this study, the application of a laser scanner is investigated for the measurement of the workpiece surface before machining to gather the required data for the adjustment of the working distance during Jet-EC machining of complicated surfaces